Ecto-nucleotide pyrophosphatase modulates the purinoceptor-mediated signaltransduction and is inhibited by purinoceptor antagonists

1 The effect of ecto-nucleotide pyrophosphatase (ecto-NPPase; EC 3.6.1.9) o n the ATP- and ADP-mediated receptor activation was studied in rat CG gliom a cells. The P2-purinoceptor antagonists pyridoxalphosphate-6-azophenyl-2', 4'-disulphonic acid (PPADS) and reactive blue (RB2) are potent inhibitors ( IC50=12+/-3 mu M) of the latter enzyme. 4,4'-diisothiocyanatostilbene-2,2' disulfonic acid (DIDS), 5'-phosphoadenosine 3'-phosphate (PAP) and suramin were less potent inhibitors with an IC50 Of 22+/-4, 36+/-7 and 72+/-11 mu M respectively. 2 P1-purinoceptor antagonists CGS 15943, cyclo-pentyl theophylline (CTP) an d theophylline did not affect the activity of the ecto-NPPase. 3 ATP- and ADP-mediated P2Y(1)-like receptor activation inhibited the (-)-i soproterenol-induced increase of intracellular cyclic AMP concentration. PP ADS, an ineffective P2Y-antagonist in C6, potentiated the ATP and ADP effec t approximately 3 fold due to inhibition of nucleotide hydrolysis by the ec to-NPPase. 4 We conclude that ecto-NPPase has a modulatory effect on purinoceptor-medi ated signalling in C6 glioma cell cultures.